I’m not one for the large illusions, but to my mind Robert Harbin’s Zig-Zag Girl is the greatest magic stage illusion ever. It’s simple, understandable, and utterly impossible looking. Doug Henning made it popular, performing it in his Broadway show The Magic Show, and for a while in the 1970s it seemed like every illusion show featured it (often without the approval of Harbin). However, these things go in cycles, and it’s not seen as often, modern day performers going for more glitz. To my mind, the low-tech look of the Harbin prop is part of its charm.
Click on the video to watch Harbin himself performing it. You can tell that this was a relatively early version of the prop as it still retains a cross bar that the assistant has to duck under, an element which Doug Henning’s design managed to eliminate.